<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>CSS mask-composite reference</title>
    <link rel="author" title="CJ Ku" href="mailto:cku@mozilla.com">
    <link rel="author" title="Mozilla" href="https://www.mozilla.org">
    <style type="text/css">
      div {
        position: absolute;
        margin: 0px;
        padding: 0px;
        width: 100px;
        height: 100px;
        top: 10px;
      }

      div.add {
        left: 10px;
        background-color: blue;
      }

      div.subtract {
        left: 120px;
        background-image: url(support/blue-100x50-transparent-100x50.svg);
      }

      div.exclude {
        left: 340px;
        background-color: blue;
      }
    </style>
  </head>
  <body>
    <div class="add"></div>
    <div class="subtract"></div>
    <div class="exclude"></div>
  </body>
</html>